1. Field of the Invention
The present invention relates to a prepreg for fiber reinforced plastic and a production process of the prepreg.
2. Prior Art
FRP is generally a fiber reinforced type plastic (fiber reinforced plastic) having a continuous fibrous material contained therein. It has a hardness comparable to that of ceramic, has a strength equal to that of metals, weighs about one fifth of iron, and has a modulus of elasticity about 3 to 4 times as much as that of iron. For such FRP, particularly CFRP (carbon fiber reinforced plastic, which may be included in “FRP”), an increase in the packing density of fibers and a resin per cross-sectional area of it has conventionally been an important research problem.
A proportion of fibers determines the strength of FRP. FRP containing an increased proportion of fibers has excellent strength, but a proper amount of a resin must be added in order to mold or form the FRP into a desired shape such as plate. The resin is also necessary for adhering fibers to each other. FRP has various kinds, depending on the weaving manner or twisting manner of fibers. For example, a cloth of about 10 m wide can be used as the fiber for FRP and such FRP is utilized for a plate or pipe of large-sized structures.
When producing such FRP, a fibrous material must be impregnated with a resin. The fibrous material can be impregnated better with a thermosetting resin than a thermoplastic resin. The thermosetting resin usually has a low viscosity so that use of it enables the production of fine and dense FRP and, in addition, its strength can be maintained high.
However, when FRP is produced in a conventional manner by using a thermosetting resin having shape memory properties, curing of the resin, for example, a two-part curing type resin, occurs as soon as mixing. In other words, the resin has a short pot life.
It was therefore impossible to process a fibrous material, which had been impregnated in advance with a thermosetting resin, after some storage time. In other words, a fibrous material impregnated with a thermosetting resin had to be molded or formed into a desired shape just after impregnation. In practice, application of FRP can be expanded if a fibrous material impregnated in advance with a thermosetting resin can be molded or formed into a desired shape at any molding or forming site.
In light of the above-described problem, the present inventors have carried out an extensive investigation on a prepreg for FRP having a sufficient pot life and permitting convenient production of an FRP molding, and a production process of the prepreg.
As a result, it has been found that the above-described problem will be overcome by a prepreg for FRP available by impregnating a fibrous material with a shape memory polymer having a specific composition, leading to the completion of the present invention.